BSc - MSc (Int.)

The study on the "Effect of chitosan application on physiological, biochemical
and molecular characteristics of Piper longum L." was carried out in the Department of
Plant Biotechnology and Department of Plantation Crops and Spices, College of
Agriculture, Vellayani, Thiruvananthapuram, Kerala during 2021-2022. The objective of
the study was to investigate the physiological, biochemical and molecular responses of
Piper longum to foliar application of chitosan (CHT).
The plants raised from the rooted cuttings of long pepper variety, Viswam were
exposed to foliar spray with varying concentrations of chitosan (1 g L-1
, 2 g L-1
, 3 g L-1
, 4
g L-1
) at 2, 4, and 6 months after planting (MAP). The control plants were devoid of
chitosan application. The study was carried out in a completely randomized design
(CRD) with four replications. The observations were taken on plant growth,
physiological and biochemical parameters and molecular characteristics.
The plant growth parameters recorded at 3, 5 and 7 MAP, showed significant
variation among the treatments tried. CHT 1 g L-1
recorded significantly higher values for
the growth parameters at all stages of observation. At 7 MAP, the foliar treatment with
CHT 1 g L-1
recorded the highest values for plant height (194.75 cm), number of primary
branches (7.75), number of spike-bearing branches (8.5), days to emergence of the spike
(73.78 days), days to flowering (20.40 days) and days from emergence to maturity of the
spike (59.83 days).
The physiological parameters at 3, 5, and 7 MAP, showed significant variation
among the chitosan foliar spray treatments. The data on physiological parameters showed
a similar trend at all stages of observation with CHT 1 g L-1
, recording the highest values.
At 7 MAP, CHT 1 g L-1
showed significantly higher values (496.50 m moles m-2
s
-1
,
247.75 mm-2
, 8.87 µmol CO2 m-2
s
-1
, and 6.83 mmol CO2 mol-1 H2O, respectively) for
stomatal conductance, stomatal distribution, photosynthetic rate and water use efficiency.
With respect to enzyme activity, the highest peroxidase (19.86 activity g-1 min-1
) and
103
catalase (933.48 activity g-1 min-1
) activities were observed at 7 MAP, in plants subjected
to chitosan foliar spray with CHT 1 g L-1
. At 7 MAP, the highest value (1.87 mg g-1
) of
chlorophyll content was also observed in the treatment with CHT 1 g L-1
.
The oleoresin, volatile oil and piperine contents obtained from mature dark green
dried and powdered spike showed significant differences among the chitosan foliar spray
treatments tried. The foliar spray with CHT 1 g L-1
gave significantly higher values with
respect to oleoresin (10.70 per cent), piperine (1.34 per cent) and volatile oil (1.46 per
cent) content.
The yield parameters viz., the number of spikes per plant, girth and length of the
spike, spike yield per plant and root yield per plant significantly varied with respect to
various chitosan foliar spray treatments. Treatment with CHT 1 g L-1 was observed to be
significantly superior with respect to the number of spikes per plant (181.5), girth of the
spike (9.997 mm), length of the spike (3.25 mm), spike yield (fresh-163.35 g plant-1
; dry31.81g plant-1
) and root yield (fresh- 47.08g plant-1
; dry-8.24g plant-1
), among all the
treatments tried. The driage however, did not show any significant variation among the
treatments.
The molecular analysis of Piper longum was done using the leaf samples
collected 24 h after the application of foliar spray at 4 MAP. RNA isolated from the
sample was used for cDNA synthesis followed by RT-qPCR. The relative fold change
analyzed using Ct values showed upregulation of the piperine synthase gene in treatment
CHT 1 g L-1
(1.87 fold) and CHT 2 g L-1
(1.34 fold) with respect to control treatment.
The chitosan foliar spray at higher concentrations of CHT (3 g L-1
and 4 g L-1
)
was observed to be inhibitory, giving a lower performance, even lower than the control
treatment, with respect to the various parameters studied.
The study confirmed that foliar spray of CHT at concentrations 1 g L-1
and 2 g L-1
,
at 2, 4 and 6 MAP could effectively enhance plant growth, physiological, biochemical,
molecular, and yield characteristics. However, the best performance was observed in the
104
lowest concentration of chitosan tried, 1 g L-1
. The foliar application of CHT 1 g L
-1
gave
maximum enhancement in piperine content, oleoresin, volatile oil, spike yield, and root
yield with an increase of 37.46, 25.86, 5.77, 21.72, and 31.6 per cent, respectively over
the control treatment. The molecular basis of increase in piperine content was studied by
RT-PCR using piperine synthase primer showed upregulation of piperine synthase gene
under CHT application at 1 g L-1
.
The results of the study indicated that chitosan, a non-toxic and ecofriendly
biopolymer has the potential for substantial enhancement of yield and quality of the
commercially exploited medicinal plant, Piper longum. The mechanism of action of
chitosan to this effect is yet to be clearly elucidated.